The present invention relates to a tensioning device for a traction element drive, such as a belt or chain drive, with a tensioning arm, which can pivot relative to a body about a pivot axle and on whose distal end a roller is rotatably supported for tensioning the traction element, by means of which a torsion spring acting between the pivot axle of the tensioning arm and the body is provided and the pivot axle is supported so that it can slide by at least one radial-bearing arrangement and at least one axial-bearing arrangement, wherein the axial-bearing arrangement comprises a friction disk arranged concentric to the pivot axle.
Tensioning devices of the type of interest here are used, in particular, for tensioning traction element drives arranged between the crankshaft and the camshaft of an internal combustion engine. The tensioning devices are exposed to considerable dynamic loading, wherein an essential goal in constructing such tensioning devices is to implement the tensioning arm that can rotate about the pivot axle so that it is not sensitive to vibrations. Therefore, according to the state of the art, friction-bearing arrangements are known, which damp or absorb the vibrations introduced into the tensioning arm via the roller supported so that it can rotate. The axial-bearing arrangement is therefore used, in particular, as a friction mechanism.
From the laid-open, unexamined application DE 44 31 801 A1, a tensioning device for traction element drives, such as belts or chains, is known. This device is comprised of a tensioning arm, which is supported rotatably and spring mounted via a torsion spring against the traction element. Tensioning means, in particular in the form of a rotatably supported roller, are tensioned by this tensioning arm. Furthermore, at least one friction element is provided between two flanges, of which one is fixed to the tensioning arm and the other is fixed to the housing. One radial flange is provided on the end with wedge-shaped ramps following one after the other in the circumferential direction, wherein a friction disk, which is arranged between the radial flanges and which can rotate relative to these two radial flanges, is provided with counter ramps that are parallel to the first ramps and thus interact with them. Thus, as a result of the wedge effect, due to a rotation of the ramps relative to each other, the tensioning pressure between the radial flanges is increased against the torsion spring, but the friction surfaces of each ramp are exposed to considerable surface pressure and are therefore subjected to significant wear. The cause of the wear lies especially in that the pressure-force component of the torsion spring presses the ramps approximately flat against each other and pressure forces caused by the compression of the torsion spring are even increased.
From Patent No. DE 43 43 429 C2, a tensioning device for a belt or chain drive is known with a tensioning arm, which carries on its end a tensioning roller and which is supported rotatably on its other end by a shaft in a housing and which is spring mounted on the housing by a torsion spring. The tensioning device disclosed here is further constructed with a friction disk locked in rotation with the shaft or the tensioning arm, between whose friction surface and an axial contact surface of the housing there is a friction lining, wherein the contact surface of the housing has a plurality of sharp-edged projections, which extend in the axial direction and which dig into the friction lining under axial pressure. In this way it is guaranteed that the friction lining is fixed in a given position on the contact surface, so that the friction work can take place only between the friction disk and the friction lining. However, according to the construction disclosed here, the friction disk has a flat contact surface running against the housing of the tensioning device. During long operation of the tensioning device, a relatively smooth friction surface is formed, so that the friction resistance that can be generated in the rotational movement of the tensioning arm has only very small values. Satisfactory damping of introduced vibrations in the tensioning arm cannot be achieved over a long operating period.